1. Field of the Invention
The present invention relates to microfluidic structures. In one example, the present invention relates to membrane valves and structures that control microfluidic flow and that can be combined to perform complex pneumatic logical operations.
2. Description of Related Art
Modern microfluidic analysis devices having evolved considerably from early single-channel, single-step devices. Highly-parallel, multi-channel devices now increase throughput by performing hundreds of assays simultaneously, and lab-on-a-chip devices now integrate complex multi-step preparation and analysis operations into a single portable analyzer. Devices that densely integrate both serial and parallel operations on-chip promise to dramatically cut the time and resources required to perform a variety of assays. For example, in the field of genomics, the integration of operations like colony picking, sequencing sample amplification, purification, and electrophoretic analysis into a high-throughput parallel platform will result in significant decreases in overall sequencing time and cost.
Realization of this goal has been slowed by the lack of valving and pumping technologies suitable for use in highly-serial, highly-parallel microdevices. These devices may require hundreds of valves to be actuated in parallel, while simultaneously hundreds of other valves are actuated one-by-one—an extremely demanding set of requirements. Part of the solution was offered by monolithic membrane valves and pumps, which can be fabricated in dense arrays and actuated in parallel via integrated pneumatic channels. However, each independent monolithic membrane valve or set of valves requires a dedicated switchable pressure/vacuum source (typically a solenoid valve) and a separate pneumatic connection to the microfluidic device. The power consumption, cost, and size of solenoid valves preclude their use in large numbers, and excessive pneumatic connections to the microfluidic device waste useful on-chip space.
A single control signal could be used to control several on-chip valves if 1) a demultiplexer is used to address which valve to open or close, and 2) each valve remains latched in its current state (open or closed) until it is set to a new state. Existing latching microvalves use bistable, buckled membranes or magnets to control flow. These silicon- or polymer-based valves are chemically and physically unsuitable for many lab-on-a-chip assays, are complex to fabricate, and cannot be easily arrayed for parallel or multiplexed actuation. Previous demultiplexers allow for addressing of individual microreactors in an array but not the more-useful, arbitrary control of independent valves. Also, the row/column addressing method employed previously imposes significant restrictions on the geometry of the device and limits the number of microreactors addressable by n control lines to only 2(n/2).